The present invention relates to a CRT electron gun; particularly, it relates to a CRT electron gun that allows current for a screen to be obtained at a high sensitivity to a driving voltage.
Hereinbelow, a description will be given of a conventional CRT electron gun. Matters such as operational conditions will be described with reference to a CRT, which is called a display monitor tube, used for computers and the like. FIG. 8 is a cross-sectional configuration view showing the vicinity of a cathode of a conventional CRT electron gun. In the figure, 1 denotes a cathode for inducing electrons toward a screen, 2 denotes an electron current, 3 denotes a G1 electrode, 4 denotes a G2 electrode, 5 denotes a G3 electrode, and 6 denotes an electron-emitting material provided on a surface of the cathode. In addition, in the conventional electron gun are provided other components, although they are not shown in the figure. For example, there are provided electrodes subsequent to the G3 electrode 5, a G4 electrode, and a G5 electrode. In addition, there are provided overall-configuration items, for example, bead glass pieces for supporting the individual electrodes.
According to the configuration of the present embodiment, the electron gun that allows current for the screen to be drawn at a high sensitivity to the cathode driving voltage can be obtained the same as in Embodiment 1 and, in addition, allows the following effects to be obtained. First of all, electrons are not emitted from a cathode-surface of a portion covered by a metal plate 7, but electrons are emitted only from a portion corresponding to the opening, that is the electron-passing opening; therefore, a load exerting on the cathode can be reduced. In addition, since electrons flowing to the G2 electrode decrease, evaporation of bas that can cause damage on the cathode can be reduced. Futhermore, power consumption can be reduced.
FIG. 9 is an explanatory drawing showing the relationship between a driving voltage and an emission current regarding the conventional CRT electron gun. In the figure, the horizontal axis represents a cathode-modulation voltage (V), which is a variation potential varied from a cathode potential at which the emission current becomes zero; and the vertical axis represents the emission current (xcexcA). While it differs depending on the size of the CRT, to cause a certain pixel to be luminous at a desired maximum luminance (for example, 100 nit), for example, an electron current of 300 xcexcA must be caused to flow to the screen. In the conventional electron gun, however, to cause the emission current to vary in a range of 0 to 300 xcexcA, the cathode voltage must be varied by, for example, about 45 V from about 120 V to about 75 V.
In many cases, individual electron-passing openings in each of a G1 electrode and a G2 electrode are circular, and the central axes of the electron-passing openings are the same. The central axis, which can be assumed to be a rotation-symmetrical axis, is represented by a Z axis. FIG. 10 is an explanatory drawing showing a potential distribution on the Z axis in the vicinity of the cathode in the conventional CRT electron gun when the emission current has reached a level of 300 xcexcA. A surface of the cathode 1 is assumed to be zero, and the direction of the screen is assumed to be positive. In the figure, the horizontal axis represents the position (mm) on the Z axis from the cathode face in the direction of the screen, and the vertical axis represents the potential (V) on the Z axis. As can be calculated according to a solid line in the graph in the FIG. 10, to obtain the emission current of 300 xcexcA in the conventional electron gun, an electric field of a 105(V/m) order exists on a front face of the cathode.
Generally, during use of the electron gun under appropriate operational conditions, much electrons exist on the surface of the cathode 1, in which the larger the electric field is applied, the greater amount of current can be obtained; and when the electric field is reduced to be lower than zero, the emission current becomes zero. While the electric field applied to the surface of the cathode can be varied according to the cathode potential, to vary the emission current in the range of 0 to 300 xcexcA, as described above, the cathode potential must be varied by about 45 V.
As described above, according to the conventional CRT electron gun, compared to a liquid-crystal display, a potential difference of as big as about 45 V must be generated to control the electron current in cases of, for example, 75 V for performing display at the maximum luminance of 100 nit, and 120 V for displaying a black color. Therefore, the conventional CRT electron gun requires a great power to be driven, causing a problem in that, since the width of about 45 V is driven at a high speed, unnecessary electromagnetic waves increase. In addition, in recent years, since even higher resolution display is demanded, the frequency of video signals needs to be even higher; however, an expensive driver circuit is required to implement high-frequency control for a driving voltage of about 45 V.
In addition, recently, demands are increasing for display monitor tubes to display motion images, but, for example, a luminance as high as 300 nit is required for comfortable observation of motion images. This causes difficulty in maintaining existing resolutions, and concurrently, in increasing the driving voltage, therefore causing difficulty in increasing the luminance.
This invention is made to solve the above-described problems caused by the CRT electron gun. An object of the present invention is to obtain an electron gun that allows electron current to be controlled with an inexpensive driver circuit at low voltages, that produces less unnecessary electromagnetic waves, and that is suitable to implement higher-frequency driving when display is performed at a luminance equivalent to a conventional luminance, and that allows current to be obtained for screens at a high sensitivity to a driving voltage that allows several multiples of the conventional luminance to be obtained when display is performed at a driving voltage equivalent to a conventional driving voltage.
The first CRT electron gun of the present invention has a cathode for emitting electrons toward a screen as a display face, a G2 electode to which a voltage higher than that of the cathode is applied, a Gm electrode to which a predetemined voltage is applied, and a G3 electrode to which a voltage higher than that of the G2 electrode is applied, wherein at least those three electrodes are provided with an electron-passing opening and are arranged on a same axis in that order from a side of the cathode, and a potential of the aforementioned cathode is varied to vary an amount of electrons to be drawn, characterized in that a lowest potential on the axis in a portion where the aforementioned Gm electrode exists substantially agrees with a maximum potential in a range where a potential of the aforementioned cathode varies, and a part of the electrons drawn from the aforementioned cathode flows into at least one of the aforementioned G2 electrode and the aforementioned Gm electrode.
According to the above, electron current can be controlled using inexpensive driving circuits and low voltages, and an electron gun producing a small amount of unnecessary electromagnetic waves can be obtained. Alternatively, an electron gun that allows a high luminance to be obtained without increasing the driving voltage can be obtained.
Also, in the second CRT electron gun according to the present invention, a mental plate that does not emit electrons is provided on a surface of the aforementioned cathode.
According to the above, a load exerting on the cathode can be reduced, electrons flowing to the G2 electrode can be reduced, evaporation of gas that can cause damage on the cathode can be reduced, and furthermore, power consumption can be reduced.
In addition, the third CRT electron gun of the present invention comprises a G1 electrode provided with an electron-passing opening to which a voltage lower than that of the aforementioned cathode is applied, between the aforementioned cathode and the aforementioned G2 electrode.
According to the above, electrons flowing to the G2 electrode can be reduced, evaporation of gas that can cause damage on the cathode can be reduced, and furthermore, power consumption can be reduced.
Furthermore, in the fourth CRT electron gun of the present invention, a screen side of the electron-passing opening of the aforementioned Gm electrode is provided with a circular portion of a larger plate thickness having a central axis identical to a central axis of the electron-passing opening.
According to the above, the diversion angle of electron can be reduced.
Still furthermore, in the fifth CRT electron gun of the present invention, a Gs electrode for preventing variations in potential distribution in the electron-passing opening of the Gm electrode is provided between the aforementioned Gm electrode and the G3 electrode.
According to the above, focus adjustment can easily be implemented.
Still furthermore, in the sixth CRT electron gun of the present invention, the same potential as that of the G2 electrode is applied to the aforementioned Gs electrode.
According to the above, voltage can be applied to the Gs electrode without increasing the number of wirings that are extended to the outside from the inside of a glass vessel of the CRT.